1. Field of the Invention
This invention relates to optical leveling devices and more specifically to optical plumb and leveling devices that utilize laser beams.
2. Description of Related Art
Conventional mechanical plumb bobs comprise a weight located at the end of a string. When the string is suspended and the position of the plumb bob stabilizes, the string defines a vertical axis due to gravity.
In recent times a series of optical plumb apparatus have been developed. For example, U.S. Pat. No. 4,448,528 (1984) to McManus describes a portable laser vertical collimator and plumb line indicator. A laser device generates a pair of beams extending at 180.degree. to each other. The laser is gimble mounted to swing freely within a wind-shielding housing and the center gravity of the apparatus lies below a gimble ring. The housing and included laser mount as a free pendulum that comes to rest with its center of gravity in vertical alignment with the intersection of perpendicular horizontal axes.
Another class of device, called level indicators or levels, includes devices with slightly arced vials with a bubble. The vials are located in a plane to define either a horizontal or vertical orientation or, with proper orientation of the vial, some other angle. Circular levels have also been provided whereby the plane of the level is horizontal when a bubble reaches an upper center portion of an enclosing cover. Some devices, such as disclosed in U.S. Pat. No. 4,720,920 (1988) to Tudek combine the conventional leveling function and electronics for producing signals when a device is level or parallel with gravity. Whereas each of these devices can define a level location in one position, it remains difficult to extend that level plane to some remote location as, from a center of a room to a remote wall.
A series of optical devices using light projectors have been developed to define a horizontal plane between a remote site and a reference site. For example, U.S. Pat. No. 3,242,340 (1966) to Layne discloses a photosensitive structure for controlling leveling and grading apparatus and for establishing levels. A mobile unit contains a radiation source that emanates light or other electro-magnetic waves in a horizontal plane. A receiver in a level determining unit indicates when the mobile station is level with the stationary station.
U.S. Pat. No. 4,841,136 (1989) to Nakayama et al. discloses a sighting apparatus that delivers a laser beam in any horizontal direction. A circular air bubble or leveling device on a table is used as input to develop a tilt signal such that the system can automatically correct for any non-horizontal orientation of the table.
Instruments also have been developed for combining the functions of plumb bobs and levelling devices using optical elements. U.S. Pat. No. 3,858,984 (1975) to Denton et al., for example, discloses an optical plumb leveler with a cylindrical housing mounted on a support by a universal joint. A weight connects to the cylindrical housing to align a beam emanating from a battery-powered lamp within the housing along a plumb line. An array of lenses condenses and projects the beam vertically. A planar mirror can be positioned in the beam to produce a 90.degree. deflection of the light beam into a horizontal plane.
In U.S. Pat. No. 4,854,704 (1989) to Funazaki et al. a light source faces upwardly from a level mounting bed. A lens extends upwardly from a mounting bed to provide a collimated parallel light rays perpendicular to a true horizontal plane. A motorized rotatable reflector device can be interposed in the light beam to produce a horizontal array.
In U.S. Pat. No. 4,993,161 (1991) to Borkovitz a laser diode mounts on a pendulous platform.
This system produces both a vertical laser beam and, by the interposition of a deflecting lens, a horizontal beam.
Each of the foregoing references discloses a plumb bob, a leveler or combination that utilizes pendulum mechanisms and optical systems that increase the overall cost of constructing such devices. Consequently, the benefits of such devices are often limited to professionals who have a need for repeated frequent use of such devices that can justify the acquisition cost. These costs effectively preclude the availability to professional or amateur carpenters who may only have an occasional need for such an optical plumb bob or leveler. Consequently many of these individuals continue to use conventional mechanical plumb bobs and mechanical leveling devices to transfer one point to another along a wall, even though such processes are time consuming and subject to error.